In order to increase the density of a magnetic recording device, the radio frequency magnetic field assisted recording scheme using a spin torque oscillator has been proposed. In this scheme, a radio frequency magnetic field is generated by the spin torque oscillator and used to locally decrease the coercivity of the magnetic recording medium. This enables magnetic recording on the magnetic recording medium having high coercivity and high magnetic anisotropy energy. Hence, thermal fluctuations are suppressed, and the recording density can be increased.
In order to increase the SN ratio of magnetic recording/reproduction, it is desired to optimize the magnetic field generated in the main magnetic pole of the magnetic recording head. However, there is a limit to optimization by improving the design of the magnetic recording head.
Conventionally, in order to increase the efficiency of the magnetic circuit to improve the writing characteristic, the distance between the main magnetic pole and the backing layer of the magnetic recording medium is designed to be as small as possible. For instance, in Non-Patent Document 1 (IEEE TRANSACTIONS ON MAGNETICS, Volume 44, Issue 11, November 2008 PP. 3376-3379, “Narrow Track Confinement by AC Field Generation Layer in Microwave Assisted Magnetic Recording” by Yuhui Tang and Jian-Gang Zhu), the distance between the main magnetic pole and the backing layer is 35-40 nm. Within the spirit of such conventional designs, there is a limit to the increase of the SN ratio of magnetic recording/reproduction.